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Transactions of the Indian Institute ofMetals ISSN 0972-2815Volume 72Number 2 Trans Indian Inst Met (2019) 72:487-500DOI 10.1007/s12666-018-1500-z

Mechanical Properties and Microstructureson Dissimilar Metal Joints of Stainless Steel301 and Aluminum Alloy 1100 by Micro-Resistance Spot Welding

Ario Sunar Baskoro, Hakam Muzakki,Gandjar Kiswanto & Winarto Winarto

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TECHNICAL PAPER

Mechanical Properties and Microstructures on Dissimilar MetalJoints of Stainless Steel 301 and Aluminum Alloy 1100 by Micro-Resistance Spot Welding

Ario Sunar Baskoro1 • Hakam Muzakki1 • Gandjar Kiswanto1 • Winarto Winarto2

Received: 12 December 2017 / Accepted: 5 November 2018 / Published online: 4 December 2018

� The Indian Institute of Metals - IIM 2018

Abstract Aluminum and stainless steel are metals that

have some mechanical property advantages. Welding

technology has been developed to join both different and

dissimilar metals applied in a construction. The property

advantages have been used to improve the performance of

a construction. However, welding performance still creates

a problem as a result of properties’ differences in metals.

This study investigated the mechanical properties of a

steel-aluminum joint with the thickness of less than 1 mm,

welded by resistance spot welding (RSW); it is called a

micro-RSW. Mechanical properties of the joint were ana-

lyzed by tensile test and were measured at the fracture area

on the tensile test specimen. Moreover, it also analyzed

intermetallic microstructure in the nugget or welding joint.

Welding time of 8 CT was an optimum parameter on a

welding process to get the maximum load. The fracto-

graphic structure of a stainless steel-aluminum joint

showed a brittle nugget. Moreover, the fracture area on the

aluminum side was larger than that of the stainless steel.

Intermetallic compound (IMC) was created by melting and

joining it through the heat input in the welding process.

IMC in SS301-AA1100 nugget affected a brittle joint.

Keywords Dissimilar metals �Micro-resistance spot welding � Mechanical properties �Fractography and microstructures

1 Introduction

Stainless steel and aluminum show such excellent mechan-

ical properties. Aluminum alloy has widely been used in

various constructions including aerospace engine parts and

electrical equipments because of its high corrosion resis-

tance, low density, and easy recyclability [1]. Stainless steel

is a potential material used in light constructions and auto-

motive apparatus because of its superb corrosion resistance,

toughness, high strength, and hardness [2]. The advantages

of both materials can be synergized in the production process

of advanced products such as medical equipment by apply-

ing dissimilar joints. Nevertheless, there are many issues

hindering the process of joining aluminum and steel directly.

They include the welding methods [3], the IMC layer

structure in the nugget, and the difficulty in developing a

bond between the two metals [4].

In order to overcome the aforementioned problems,

several strategies have been proposed. Ezazi et al.

employed laser power welding to join a piece of 1 mm

stainless steel (SS) 304 and a piece of aluminum alloy

(AA) 5085 sheet. They found out that the strengths of the

joints had doubled up to 1.48 and 1.85 times by pre-placing

the single and multi-component activating flux (oxide-

based TiO2 and halide-based CaF2 flux powders) on the

surface [5]. Aluminum and copper were welded through

friction stir welding. Effect of plate position, tool offset,

tool rotational speed on mechanical properties and

microstructures were studied by Sahu et al. Their study

revealed that IMC of Al–Cu was almost the same in per-

centage, with mixed flow of Al/Cu materials throughout the

nugget zone, and grain size variation in the welding nugget

[6]. The objective of their study was to find out if a defect-

free ultra-narrow multi-pass weld could be achieved by

employing pulse current gas metal arc welding process

& Ario Sunar [email protected]

1 Mechanical Engineering Department, Faculty of Engineering,

Universitas Indonesia, Kampus Baru UI, Depok 16424,

Indonesia

2 Metallurgical and Materials Engineering Department, Faculty

of Engineering, Universitas Indonesia, Kampus Baru UI,

Depok 16424, Indonesia

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Trans Indian Inst Met (2019) 72(2):487–500

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with vertically placed electrode depositing single bead per

layer in weld groove. Simultaneous effect of significant

decrease in joints’ surface depression led to welds’

geometry improvement in addition to less formation of

interfacial Fe–Al intermetallic, which were the major cause

for considerable strength improvement [5]. Ultrasonic

welding was also used to join aluminum–copper, and dif-

ferent recrystallization behavior was observed on alu-

minum and copper surface region [7]. Satpathy and Sahoo

studied microstructural and mechanical performances of

ultrasonic spot welding of aluminum to copper joint. They

found out that the tensile shear and T-peel failure load had

increased in accordance with the specifically reached

welding time [8]. A fiber laser welding process was

employed by Kuryntsev et al. to join butt austenitic steel to

commercially pure copper. The findings revealed that the

electrical resistivity coefficient of copper–SS weld was

higher than that of SS. The width of intermediate layer

between SS and copper was 41–53 lm, respectively [9].Dissimilar materials, that were a piece of 0.8 mm A6061A-

P6 and a piece of 0.5 mm SUS 304 were joined by a punch-

joined process [10]. Moreover, they also studied the ther-

moplastic process and the joining performance, parameters,

and tool geometry on the static tensile shear strength and

peel strength on the single-lap joint. Friction stir riveting

extrusion was employed to join a piece of 1 mm Al 6061 on

aluminum plates and a piece of 1.5 mm low-carbon steel

[4]. Mehta and Badheka [11] welded copper to aluminum

by employing the friction stir welding technology which

had been threatened by the preheating and cooling process.

They found out that the amount of intermetallic compounds

formed in stir area had increased because of the preheating

current, and the cooling treatment had led to a significant

intermetallic decrease.

RSW is a welding technology which can join different

kinds of metals. This welding generates heat to melt base

metal (BM) because of electrical current flow in metal

surface [12], and it depends on the metal resistivity. RSW

is generally employed in industrial sectors to join metal

sheets due to its simple welding process. Kang et al. [13]

studied fatigue properties of aural2 to aluminum alloy on

resistance spot of the welding nugget. The findings

revealed that the adhesive addition increased the nugget

size and the main fatigue crack had initiated at the edge of

the nugget on aural2 surface. RSW was used by Sun et al.

to join aluminum (AA 5754) and magnesium (AZ31)

alloys. They studied mechanical properties and

microstructures of a nugget [14]. Zhang et al. [15] opti-

mized an RSW electrode to join aluminum alloy and gal-

vanized high-strength steel. The findings revealed that the

welded joint could be achieved by optimizing the elec-

trodes due to a special weld–brazed joint, and an inter-

metallic compound layer with maximum thickness, the size

of which was about 4.0 lm was installed in the aluminumand steel interface in the welded joint. Zhang et al. [15]

welded a dual-phase 780 steel sheet the thickness of which

was 1.2 mm thickness to a dual-phase 600 steel sheet the

thickness of which was 1.5 mm using RSW. The proposed

hypothesis was that, tensile stress affected interfacial fail-

ure and shear stress affected pullout failure. RSW was

applied by Xinjian Yuan et al. [16] to join ultra-low-carbon

DC54D the thickness of which was 1.0 mm and DP600

steel the thickness of which was 1.6 mm. Austenitic

stainless steel and ferritic stainless steel sheet joined by

RSW was also studied by Bina et al. [17]. They found out

that the 9 kA welding current, the 14-cycles welding time,

and the 2.6 kN electrode force generated a 6.59 kN max-

imum load. The dissimilar spot welding resistances of a

piece of 16-Mn-high-strength steel the thickness of which

was 1.0 mm and a piece of 6063-T6 aluminum alloy plate,

the thickness of which was 1.5 mm were studied by using

different welding electrodes and welding parameters.

When the optimum welding electrode was employed, its

effects to the tensile strength went up and its effects to its

indentation ratio went down because of the temperature

distribution and weld quality improvement. Joining of less-

than-1-mm-thick metal sheets employing friction stir spot

welding (FSSW) is called micro-FSSW [18]. Papaefthy-

miou et al. [19] also studied micro-friction stir welding.

Spot welding resistance employed to join less-than-1-mm-

thick metal sheets is defined as micro-RSW [20]. Dissim-

ilar micro-resistance spot welding of Al 1100-KS 5 spring

steel has been conducted by Baskoro [20]. The welding

current effects on micro-properties were very slight;

moreover, the welding current highly depended on the size

of the nugget [21]. This study investigated micro-RSW to

join dissimilar stainless steel 301(SS301) materials and

aluminum alloy 1100 (AA1100), where welding parame-

ters of micro-RSW significantly influenced the nugget

quality.

Joining dissimilar metals has still created not only

mechanical problems but also problems in the thermal and

physical properties. Problems of joining dissimilar SS301

and AA1100 metal sheets lie on the intermetallic phase in

the joint area. Furthermore, it is more difficult to provide a

better mechanical property of welding joint in the micro-

RSW. There are not many researchers who have studied

this problem. Welding parameters are important factors to

maintain a mechanical property of welding joint. Welding

parameters affect the melting processes of both SS301 and

AA1100 where the thermal and physical properties differ.

A micro-RSW for a piece of SS301 sheet and a piece of

AA1100 sheet is interesting topics to study. The mechan-

ical properties have been studied by employing the tensile

test and fractographic and microstructure analysis.

123

488 Trans Indian Inst Met (2019) 72(2):487–500


2 Methods of Experiments

2.1 Materials

Two materials employed in this study were a piece of

200-lm-thick stainless steel 301 sheet and a piece of400-lm-thick aluminum alloy 1100 sheet. The chemicalcompositions of both materials are shown in Table 1.

American Welding Society (AWS) is an American

welding association whose members consist of practition-

ers, scientists, and researchers who are experts in welding.

Welding technology is very broad and has unique charac-

teristics. And by using the standard testing process from

AWS, it will get more precise or more valid results [22].

Both materials were then cut according to AWS dimension

standard [23] that was 76 mm in length, 19 mm in width,

and 19 mm in overlap. Schematic of welded specimen is

shown in Fig. 1. The specimens were subsequently washed

by acetone solution. The detail of experimental works has

been outlined elsewhere [22].

2.2 Welding Process

Specimens were welded by RSW machine with AC

230/240 V, ? 15%, - 20% single-phase input voltage, 65

kA input current, and 8 kA maximum welding current. An

overlap joint was employed for the joining design, where

SS301 was placed on top of AA1100. This study employed

5 kA and 8 kA as welding current and varied the welding

time of 6, 8, and 10 cycle time (CT) as specimen code

shown in Table 2. Welding force and holding time were

assumed constant. Each welding parameter used 30 spec-

imens; 27 specimens were characterized with tensile tests

and fractographic analysis, and three other specimens were

used for microstructure analysis.

2.3 Tensile Test

Welded specimens were tensile-tested. Specifications of

machine RTF-2350 employed were as follows: 50 kN

maximum capacity, 798 mm effective stroke,

0.0005–1000 mm/min crosshead speed, ± 0.1% speed

accuracy, and load measurement accuracy of 0.5% of

indicated value. The data of tensile-test was recorded by

the machine computer, and the data was saved in Excel

format. The resultant data represented the effects of load

and elongation.

Because the area and the thickness of weld nugget was

so thin, therefore the setting parameter of tensile test

machine [8] was crucial to get a precision result. Some

parameters were 5000 N load cell rating, 1 mm/min test

speed, maximum point, upper yield, and break point.

Tensile test was employed to measure the weld nugget’s

load and elongation.

2.4 Fractographic Analysis

A fracture on a specimen of micro-RSW after the tensile

test represented the welding joint performance. The pur-

pose of this analysis was to know the weld nugget condi-

tion, the mixing of metal melt and cooling condition

leading to the joint condition. When the mixing of both

parent metals was better, it affected the tear or fracture of

the weld nugget. The weld nugget without hole or fracture

revealed the fact that the weld nugget was brittle or the

mixing of parent metals was not good enough.

The effects of tensile test on nugget were analyzed and

measured. There were two kinds of failure: interfacial

failure and pullout failure. Interfacial failure was tensile-

tested specimens failed on both surface, and pullout failure

was tear or fracture on the weld nugget [24]. Crack or

fracture zone was analyzed on the SS301 or AA1100 side

using visualization. When the analyzed result showed a

hole, it was analyzed by image analysis using digital

microscope and then it was measured [25] by using a

software of a microscope. Gibson et al. [26] also used this

method to analyze a failed welding. The flowchart of

analyzed specimen is shown in Fig. 2.

Each hole of the tensile-tested specimen was measured

by a digital microscope; it was supported by a software

which could measure the area of the crack or fracture of

Fig. 1 Welded sample schematic

Table 1 Chemical composition of observed materials

SS301 80% Fe 0.14.5% C 18% Cr 1% Si 2% Mn 0.045% P 6-8% Ni 0.03% S

AA1100 99% Al 0.0008% Be 0.20% Cu 0.95% Si ? Fe 0.050% Mn 0.10% Zn – –

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Trans Indian Inst Met (2019) 72(2):487–500 489


tensile-tested effect [27, 28]. The fracture zone was

zoomed to 20x and a measurement result of specimen is

presented in Fig. 3.

Measurement results of specimens were summarized,

and the crack or hole on interface was analyzed and dis-

cussed. Mechanical properties were influenced by the heat

input because of the change of microstructure; therefore,

the hardness of nugget was also changed.

2.5 Micro-hardness

Specimens casted by resin were cut along the center of the

spot of weld nugget in the direction of the width of the

sample. The cross section of the weld nugget in the resin

was polished and then was etched [27, 29]. The specimens

were polished by aluminum chloride-dissolved water and

etched by nital etchant solution. Specimen preparation for

microstructure analysis is presented in Fig. 4. Specimens

were used for micro-hardness and microstructure analysis.

Metallographic preparation was performed before the

microstructure of nugget could be analyzed. Some regions

were inspected by digital microscope such as base metal,

heat-affected zone (HAZ), and intermetallic. Each region

was measured using hardness tester with the indenter load

of 25 g. The change of the microstructure was analyzed by

using SEM and EDS to know the chemical composition in

the intermetallic.

2.6 Microstructural Analysis

Microstructural analysis was employed to know the new

microstructure development of a weld nugget affected by

the melting, mixing, and cooling of micro-RSW processes.

The results of scanning electron microscope (SEM) rep-

resented different microstructure images of weld nugget

and microstructure of parent metals and also showed the

intermetallic compounds of dissimilar metal in the weld

nugget. An energy dispersive X-ray spectroscopy (EDS)

was used to measure chemical composition.

The prepared specimens were analyzed with the weld

nugget in the resin zoomed 200x by digital microscope,

and intermetallic SS301–AA1100 was analyzed. The joint

feature and chemical composition of IMC were studied.

JSM-6510 SEM of JEOL equipped with an energy dis-

persive X-ray spectroscopy (EDS) was used to study the

new microstructure and chemical composition of the nug-

get. Microstructure analysis represented the IMC and

chemical composition in the nugget.

Fig. 2 Fractographic analysisprocess

Fig. 3 Measured specimen

Table 2 Welding parameters and sample code

No. Applied welding current (kA) Cycle time (CT) Sample code

1 5 6 SS-AA-56

2 8 SS-AA-58

3 10 SS-AA-510

4 8 6 SS-AA-86

5 8 SS-AA-88

6 10 SS-AA-810

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3 Result and Discussion

3.1 Maximum Load

In order to reveal the mechanical properties of the weld

nugget, maximum loads have been measured by a tensile

test machine. Maximum load of the 27 tested specimens of

each welding parameter combination is shown in Table 3.

The tensile test results of each parameter combination

have been analyzed. Each welding parameter (six combi-

nations) consists of 27 tested specimen results. The highest

and lowest results show the upper and lower limit of test

results, respectively. The lowest load and elongation curve

is presented in Fig. 5.

Figure 5 shows that the elongation of all observed

samples is less than 1 mm and the weld breaking point is

close to the maximum load. For example, the lowest

maximum load of SS-AA-56 and SS-AA-810 have an

elongation length less than 0.2 mm. Figure 5 exhibits

106.9 N maximum load and 0.14 mm elongation of SS-

AA-56. The rupture of weld nugget or the break point is on

maximum load point. Maximum load point of SS-AA-58 is

145.6 N when the elongation point is 0.08 mm and the

break point occurs at 0.08 mm elongation. SS-AA-510

obtaining the lowest maximum load is 126.7 N and the

elongation is 0.08 mm. The weld joint of SS-AA-86 sep-

arates at 0.1 mm elongation and at a load of 140.9 N. It is

the lowest maximum load for SS-AA-86. SS-AA-88 shows

that the maximum load is 156.9 N and elongation is

0.08 mm, where this elongation resembles with SS-AA-

510, in maximum load position. Figure 5 explains that SS-

AA-810 shows 152.3 N maximum load and 0.1 mm

elongation.

Figure 6 presents the highest maximum load of 27

specimens for each welding parameter. The maximum load

of SS-AA-56 at 196.4 N is the highest load of all the

specimen, and the break point is at 0.26 mm elongation.

The highest maximum load of SS-AA-58 and elongation

value are 251.9 N and 0.18 mm. It shows that break point

is near maximum load point. The highest maximum load

for SS-AA-58 in Fig. 6 appears like the lowest maximum

load for SS-AA-58 in Fig. 5, which is the break point in

maximum load point. Figure 6 shows that the highest

maximum load of SS-AA-510 is 187.7 N with the elon-

gation of 0.225 mm, and the elongation at the break point

is 0.385 mm. SS-AA-86 leads to 211.4 N maximum load

when the elongation value is 0.219 mm, and it exhibits

break point at 0.238 mm. The highest maximum load for

SS-AA-88 presented is 260.3 N at an elongation of

0.235 mm and break point is on elongation length of

0.32 mm. The highest maximum load of SS-AA-810 is

obtained as 244 N when elongation is 0.199 mm which

also shows its break point.

Figure 6 reveals that the highest of SS-AA-510 and the

highest of SS-AA-88 have long elongation in the weld

nugget. Figures 5 and 6 explain the break point near the

maximum load value. It shows that the nugget of SS301

and AA1100 weld by micro-RSW is brittle. SS301 is low-

carbon steel, and Fe composition leads to brittle weld in the

nugget when a joint of SS301–AA1100 melts and then cool

down to room temperature. Cooling process affects

microstructure composition.

The average values of the lowest and the highest max-

imum load of each weld parameter are measured for easy

analysis of maximum load trend of each weld parameter.

The highest, lowest, and average maximum loads are

shown in Fig. 7.

The maximum load of welding time 6 CT at 5 kA and 8

kA is lower than 8 CT and 10 CT. Maximum load at

welding time 8 CT tends to increase; the significant

increase is highest for 8 kA. Maximum load at welding

time 10 CT tends to decrease; maximum load at welding

time 10 CT for 5 kA decreases significantly. This trend is

similar with Xinjian Yuan et al. This result can be inter-

preted that welding time from 6 CT to 10 CT at 5 kA and

welding time more than 8 CT at 8 kA leaded to heat input

Fig. 4 Microstructure sample preparation and analysis process

123



which spread in spot. Welding time 10 CT at 5 kA and 8

kA or more affect overlarge indentation [16]. Optimized

welding time and welding current combination influence

mechanical properties.

3.2 Fracture Analysis

Weld nugget performance can be studied by fracture on

weld nugget when the load rupture the weld joint. Tensile-

test damages in steel-aluminum joint, can be studied about

Fig. 5 Lowest peak load of each welding parameters Fig. 6 Highest peak load of each welding parameters

Table 3 Peak load of tensile test results in newton (N)

SS-AA-56 SS-AA-58 SS-AA-510 SS-AA-86 SS-AA-88 SS-AA-810

155.39 183.16 126.67 160.57 156.90 178.76

158.35 178.11 151.06 184.81 224.43 152.34

150.38 155.29 174.02 180.25 198.37 163.64

133.59 157.77 131.83 184.64 204.32 234.51

121.71 154.64 154.94 194.14 188.05 152.42

160.48 149.23 137.81 158.31 215.63 207.37

146.14 218.56 187.70 161.02 181.93 163.90

106.87 206.05 175.75 156.14 193.65 167.18

137.59 159.43 173.70 168.55 241.90 194.93

129.15 145.62 148.68 162.58 231.19 175.18

142.45 231.84 171.85 162.12 177.87 216.24

161.62 160.62 161.15 204.46 211.97 228.57

115.26 214.48 178.04 204.46 215.75 208.78

196.40 211.35 172.93 157.56 175.00 170.24

128.64 210.22 164.51 157.56 225.12 170.24

146.98 148.76 162.65 159.44 188.49 158.23

163.16 251.89 178.41 152.93 193.48 161.66

146.72 216.65 170.62 176.84 260.26 244.06

142.93 249.76 143.66 141.00 165.76 195.94

134.80 226.85 172.38 184.79 197.35 159.22

154.23 170.08 138.96 143.90 217.07 205.48

142.01 215.26 171.24 187.43 206.58 157.56

151.73 217.95 184.61 140.42 204.20 235.87

177.35 195.15 166.23 208.89 170.76 200.31

143.49 162.43 150.81 153.76 194.34 229.52

115.97 154.56 176.24 209.74 199.05 195.03

175.63 181.14 139.67 182.69 190.14 193.68

123



the fracture condition to get information about the ductility

of weld nugget. Weld parameters of twenty-seven speci-

mens have been tensile-tested, and the specimens break

into two pieces: aluminum and steel. So 54 pieces of alu-

minum and steel have been analyzed and examined by a

digital microscope. The result of measurement and analysis

shows that not all specimens are broken or have a hole. The

rupture of specimens and their measured fracture area are

shown in Figs. 8, 9, 10, 11, 12, and 13.

The fracture condition is not only on stainless steel side

but also on aluminum side. Fig. 8 reveals area and condi-

tion of fracture on each rupture specimens. In SS-AA-56

four pieces out of 54 pieces leads to fracture on only alu-

minum side. The fracture areas on four specimens are

0.372 mm2, 0.428 mm2, 0.323 mm2, and 1.102 mm2, and

the fracture conditions are revealed in Fig. 8.

The specimen code of SS-AA-58 with the welding

process of 5 kA and 8 CT produces fracture on seven

pieces of specimens. The fractured positions are four pieces

on aluminum and three pieces on stainless steel. The

fracture areas of the aluminum side are 0.752 mm2,

1.110 mm2, 0.066 mm2, and 0.026 mm2, and the fracture

conditions are shown in Fig. 9a–d. The fracture areas and

fracture condition of the fractures on the steel side are

exhibited in Fig. 9e–g and the fracture areas of three

specimens are 0.122 mm2, 0.62 mm2, and 0.066 mm2.

At welding parameter of 5 kA and 10 CT (SS-AA-510),

eleven pieces of fractured specimens are obtained, where

seven pieces are on aluminum side and four pieces are on

steel. The fracture condition of each piece is shown in

Fig. 10. Figure 10a–g show the fracture area on aluminum

side with the fracture areas of 1.054 mm2, 0.420 mm2,

1.131 mm2, 0.871 mm2, 0.407 mm2, 0.356 mm2, and

0.496 mm2, respectively. And in Fig. 10h–k, the fracture

area on the steel side have areas of 0.159 mm2, 0.162 mm2,

0.093 mm2 and 0.067 mm2, respectively.

The area and fracture conditions due to 8 kA and 6 CT

welding parameter in SS-AA-86 are presented in Fig. 11a–

g. There only two pieces are only fractured on aluminum

side and five pieces are fractured on steel side. The fracture

areas of 0.132 mm2 and 0.175 mm2 are on the aluminum

side and the fractures areas on the steel are 0.209 mm2,

0.187 mm2, 0.059 mm2, 0.071 mm2, and 0.067 mm2.

Fig. 7 Average of lowest and highest maximum load. a Maximum load at 5 kA, b Maximum load at 8 kA

Fig. 8 Ruptured area on AA1100 side

123



Fig. 9 Ruptured area on AA1100 and SS301 side

Fig. 10 Fracture area on AA1100 is larger than SS301 side

123



The fracture condition and fracture area of 8 kA welding

current and 8 CT welding time as in SS-AA-88 is presented

in Fig. 12a to 12e. The fractured aluminum is only in two

pieces with areas of 0.772 mm2 and 0.195 mm2. Fracture

areas of 0.063 mm2, 0.095 mm2, and 0.034 mm2 are on

steel side.

Fracture condition and fracture area of SS-AA-810 are

presented in Fig. 13a–h; four pieces are on aluminum side

with fracture areas of 0.256 mm2, 0.434 mm2, 0.155 mm2,

and 0.117 mm2, and the fracture area on the steel seed are

0.166 mm2, 0.017 mm2, 0.107 mm2, and 0.015 mm2.

These results may be attributed to the welding current

and welding time leading to heat input used to melt base

metal; melting zone rises when welding current is

increased or with additional welding time. Microstructure

changes in SS301 also affect the brittleness on SS301

Fig. 11 Fracture position on SS301 and AA1100

Fig. 12 Fracture area and crack on AA1100 and SS301

123



surface side. It can be interpreted in two aspects. Firstly

increased heat input produces large melt of both metal [30];

AA1100 is ductile, so fracture area is larger. Second, IMC

increases; it influences to easy crack.

3.3 Micro-hardness Analysis

Hardness properties affect the brittleness properties. Micro-

hardness analysis of nugget developed by AA1100 with

SS301 is present in Fig. 14.

The hardness of nugget can be measured using Vickers

method. Vickers hardness values from each zone are

measured and shown in Fig. 14. This figure represents the

hardness values of weld nuggets that are welded with

welding current of 5 kA and 8 kA and welding times of 6,

8, and 10 CT. Specimen code represents the materials,

welding current, and welding time. The indentation areas

of hardness testing are on stainless steel 301 side, HAZ in

the stainless steel side, intermetallic compound, HAZ of

the aluminum alloy AA1100, and aluminum alloy AA1100

side.

Figure 14 shows that hardness values of HAZ areas tend

to increase not only in the SS301 sides but also in the

AA1100 side. Hardness of intermetallics also tends to

increase; however, in two specimens they tend to decrease.

Hardness of HAZ in the stainless steel which is welded

with welding current of 5 kA and welding time of 6 CT

decreases, when the value is 290 HV compared to base

metal of 314 HV. In welding current of 5 kA and welding

time of 8 CT, the hardness value in HAZ of SS301

increases; moreover, with welding current of 8 kA, the

hardness value of HAZ of SS301 increases more. Hardness

values of intermetallic tend to increase. Especially the

hardness value with the welding current of 5 kA and

welding time of 10 CT and with welding current of 8 kA

and welding time of 10 CT are 373 HV and 327 HV,

respectively. These are higher than the hardness of base

metal. HAZ in AA1100 sides significantly increases than

hardness values of base metals. The average hardness value

of HAZ in AA1100 is 92 HV.

The heat input of welding process affects the changing

of microstructure around the weld nugget. When the

welding current increases from 5 to 8 kA, the hardness of

HAZ also increases; it shows that welding current improves

Fig. 13 Rupture and crack on AA1100 and SS301

Fig. 14 Results from micro-hardness measurement in the weldnugget

123



the heat input, so it makes the HAZ area wider. The

developed intermetallic has the hardness value higher than

the base metals. With the increase in the micro-hardness of

intermetallic compound, the brittle properties also

increases.

3.4 Microstructure Analysis

Microstructure of the dissimilar material’s nugget is

important to develop and to create a better welding joint.

This article have also studied the microstructure of nugget

condition or intermetallic between SS301 and AA1100 in

the nugget that has been analyzed by SEM and EDS.

Fig. 15 Intermetallic in the nugget and EDS specimen location for 5 kA

123



Nugget condition of each welding process parameter is

shown in Fig. 15. The chemical composition of IMC in the

nugget is shown in Table 4.

Figure 15a presents the SEM image of SS301 and

AA1100 joint welded by current 5 kA and time of welding

6 CT and producing an IMC layer. The IMC layer is clearly

visible. Figure 15b shows the EDS result bringing out the

chemical composition of the material. Elements, such as O,

Al, Cr, and Fe are detected. It is also observed that O

concentration is similar to that of Al. Figure 15c shows a

weld joint between SS301 and AA1100, joined by welding

current of 5 kA and welding time of 8 CT; the IMC layer is

not clear enough. Elemental chemistry of Al dominates,

and it is represented in Fig. 15d. In Figure 15e, a joint has

been welded by welding current of 5 kA and welding time

of 10 CT. It leads to the highly visible IMC layer. Fig-

ure 15f represents the elemental composition such as O,

Al, Cr, and Fe in IMC.

Figure 16a shows that the IMC layer with 8 kA welding

current and 6 CT welding time process is clearly visible.

Figure16b shows elements such as O, Al, Cr, and Fe.

Welding current and welding time of 8 kA and 8 CT

respectively affect the IMC layer. It is represented in

Fig. 16c. The IMC layer obtained form joining, by using 8

kA welding current and 10 CT welding time is the widest

one. Figure 16b, d, f shows the elemental composition of

Al, O, Cr, and Fe. C only appears in Fig. 16d. SS301 has

Fe, C, and Cr and Al dominates the composition in

AA1100. Aluminum tends to oxidize with oxygen to form

an alumina layer (Al2O3) [31–33]. Alumina affects the

intermetallic, which contains oxygen. This phenomenon is

influenced by the welding current, where the increase in

welding current leads to the growth of an IMC layer.

Table 4 shows that chemical composition of IMC in the

nugget of SS-AA-56 is strongly dominated by Fe; the

weight of Fe is 88.85% and Al is only 1.64%. Intermetallic

of SS-AA-58 has chemical composition of 76.04% Al and

14.37% Fe. While in the chemical composition of the IMC

layer in SS-AA-58 nugget, the composition of Al much

more than others. Chemical composition of Al and Fe in

the IMC of SS-AA-510 are 47.77% and 38.52%, and the

EDS does not detect Cr and C. In the IMC of SS-AA-86,

the portion of Al and Fe are similar, namely 40.5% and

46.34%. In chemical composition of SS-AA-88, portion of

C is higher than others where Al is of 0.58% only and Fe is

of 17.13%. Fe and Al portions in IMC in the SS-AA-810

nugget are similar: 45.67% Al and 40.97% Fe. Comparison

of chemical composition of AA1100 in the nugget with

AA1100 BM, it can be explained that Al portion decreased

from 99% in base metal to 83.67% in the nugget. In SS301,

the portion of Fe in base metal is 81% which become

87.58% in nuggets, with a 6.58 percent increase.

Microstructure of nugget reveals that the SS301 and

AA1100 joint welded by micro-RSW grow intermetallics

of both metals. The welding parameters affect the heat

input which leads to weld zone and changes chemical

composition. Joining interface of steel and aluminum

develops IMC that affects the mechanical properties of the

nugget.

4 Conclusions

This report reveals the study of mechanical properties and

microstructure analysis of SS301–AA1100 nugget of

micro-RSW. The following conclusions are obtained from

experimental results and discussions.

1. Joining dissimilar metals in the form of thin plates of

SS301 and AA1100 can be successfully produced by

micro-resistance spot welding.

2. Tensile test represents the break point of maximum

load. The highest of SS-AA-510 and the highest of SS-

AA-88 only have long elongation in the weld nugget.

Table 4 Chemical composition in the nugget and base metal

Specimen Al Fe Cr C O others

SS-AA-56 1.64 88.85 6.87 0 2.64 0

SS-AA-58 76.04 14.37 1.68 0 7.91 0

SS-AA-510 47.77 38.52 0 0 9.24 4.47

SS-AA-86 40.5 46.34 5.81 0 7.31 0.04

SS-AA-88 0.58 17.13 1.3 66.86 14.13 0

SS-AA-810 45.67 40.97 5 8.36 0

AA1100 in the nugget 83.67 11.19 0 0 5.14 0

SS301 in the nugget 0.81 87.58 11.61 0 0 0

AA1100 BM 99 0.95 0 0 0 0.05

SS301 BM 0 81 18 0.14 0 0.86

123



A break point near maximum load value is brittle joint.

SS301 is low-carbon steel; its Fe composition influ-

ences the weld nugget when a joint of SS301–AA1100

melts and then brought down to room temperature by

the cold process.

3. Tensile test also shows effects of welding parameters

to peak load. SS-AA-88 and SS-AA-58 have 260.3 N

and 251.9 N peak loads. However, SS-AA-510 has the

lowest peak load of 195.9 N. The peak load mentioned

above explains that combination of welding current

and time influence the peak load. Welding time

between 6 CT and 10 CT at 5 kA and welding time

more than 8 CT at 8 kA increases the heat input

spreading in various spots. Welding time 10 CT at 8

Fig. 16 Intermetallic in the nugget and EDS specimen location from 5 kA

123



kA or more results in overlarge indentation. Optimized

welding time and welding current combination affect

the nugget performance.

4. Fractographic analysis explains a nugget fracture size

of each welding parameter. The average fracture area

of 5 kA and 10 CT in aluminum side is 0.676 mm2,

and the average area of stainless steel is less than

0.2 mm2. Increased heat input produces the rising melt

of both metals; AA1100 has such ductility that the

fracture area is larger than that of SS301. Ferro

composition affects the microstructure change, so it

easily cracks.

5. Micro-hardness of HAZ of SS301 sides increases and

micro-hardness of intermetallic tend to increase;

however, the micro-hardness of weld nugget welded

by welding time of 10 CT and welding current of 5 kA

and 8 kA decrease. The hardness of HAZ in AA1100

sides increases and the hardness significantly increases

in intermetallic or IMC.

6. Microstructural analysis by SEM and EDS conclude

that the thin stainless steel and aluminum joined by

micro-RSW grow intermetallics of both metals.

Increased welding current affects the IMC improve-

ment. It also affect the mechanical properties such as a

brittle nugget. Chemical composition of IMC nugget is

dominated by Fe and Al; however, Fe portion increases

in the nugget zone.

Acknowledgement The authors would like to extend a lot ofappreciation to the Ministry of Research and Technology and Higher

Education for its financial support through the PTUPT program with

contract number of 488/UN2.R3.1/HKP05.00/2018.

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Mechanical Properties and Microstructures on Dissimilar Metal Joints of Stainless Steel 301 and Aluminum Alloy 1100 by Micro-Resistance Spot WeldingAbstractIntroductionMethods of ExperimentsMaterialsWelding ProcessTensile TestFractographic AnalysisMicro-hardnessMicrostructural Analysis

Result and DiscussionMaximum LoadFracture AnalysisMicro-hardness AnalysisMicrostructure Analysis

ConclusionsAcknowledgementReferences

fakultas teknikteknik.trunojoyo.ac.id/penelitiandosen/hakam muzakki/18... · 2019. 3. 27. ·...

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